Photosensitive glow-relay tube



April 15, 1941. P. w. BLACKBURN PHOTOSENSITIVE GLOW-RELAY TUBE Filed May31, 1959 Ilka! irlrlraldrlllllrl a!" INVENTOR P. #1. 54/76 KEV/PA BY WATTORNEY Patented Apr. 15, 1941 warn PHOTOSENSITIVE GLOW-RELAY TUBEPhilip W. Blackburn, East Orange, N. J., assignor to WestinghouseElectric & Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application May 31, 1939, Serial No. 276,62

1 Claim.

greater voltage change than heretofore possible 1 with photosensitivedevices.

Other objects and advantages of the invention will be apparent from thefollowing description and drawing in which Fig. 1 is a View, partly inelevation and partly diagrammatic, of a photosensitive tube and relay.

Figure 2 is a view on lines II-II of Figure l.

The present method of operating a photosensitive apparatus-to actuate arelay is to provide the usual commercial illuminating lamp directing itsrays upon a phototube connected to an amplifier, usually a thyratron, sothat the photoelectric current will be sufficiently amplified to operatea relay.

Several attempts have been made in the past to make a photosensitivetube capable of carrying sufficient current to directly operate therelay. Generally, such devices were provided with a very larg cathodearea with the purpose of providing a current of a few milliamperesinstead of micro-'amperes as provided by the regular phototube. When theare or glow discharge takes place in a tube with such a photosensitivesurface, the surface is soon sputtered oil", or otherwise harmed ordamaged, as far as photosensitivity is concerned.

The life of such tubes has been very short as the surface is eventuallysputtered or loses its photosensitivity. Also, because the surfaceselected is rather insensitive, a large quantity of light falling on thecathode makes only a slight change in the breakdown voltage of the tube.

To overcome these difficulties I have provided a phototube in which thegaseous atmosphere will always be very readily ionized when a lightsignal illuminates the cathode surface, and I have also selected anilluminating device for the light signal that will most easily providethe ionization of the path between the cathode and anode. In particular,I utilize a caesium cathode and a gaseous atmosphere of one or morenoble gases in which there is an excess of caesium vapor from thecathode.

Furthermore, I provide an illumination device that is strong in the blueportion of the spectrum so that the caesium will be quickly and highlyionized. The result of this combination is that he device will breakdown at avoltage much lower than that of the usual photosensitive ap-.paratus and will be capable of supplying the few milliamperes necessaryto directly operate the relay.

In Figure 1 I have illustrated the photosensitive tube It having theinterior spac H therein filled with a gaseous atmosphere of one or moreof the noble gases. This atmosphere may be of argon, or argon and neon,or any one or combination of the noble gases. I prefer to utilize apressure of from 2 to 10 millimeters of mercury pressure.

The anode it may be a cylindrical rod arising from the center of a pressl3 through which passes the anode connection M to the contact pin l5.The cathode I6 I prefer to construct as a wire mesh and to make it inthe cylindrical form disclosed in Figure 2. Two standards I! supportthis mesh from the press l3 and a connection I? to one of thesestandards extends to the cathode pin Is.

A relay 2%! to make or break the circuit 2|, 22 to any desired actuatingmechanism is connected in the leads from the electrode pins 15 and [9 toa suitable voltage line source 23 and 24 to provide the voltage drop forbreakdown of the phototube 10 when a proper light signal is received. Acontainer 25, which may be of the helmet type, is placed in the tube andpreferably connected to one of the cathode leads, as disclosed. Thishelmet has a caesium pellet therein and preferably has an excess amountof caesium therein over that utilized for the usual phototube.

This caesium is flashed after the tube has been formed and the caesiumcoats the mesh of the cathode It. The excess caesium acts as a vapor tomingle with the gaseous atmosphere of the noble gas or gases. Thecaesium may have a pressure of 1/1000 of a micron to one micron,depending upon the temperature of the device. In this respect my tubedifiers from the tubes of the prior art using similar helmets ofcaesium, because the caesium in these tubes is just sufiicient to coatthe cathode and if there should chance to be any excess Vapor, it isremoved by pumping, baking or chemical action prior to inserting thegaseous atmosphere. The prior art tubes do not have, even by chance, mydeliberate pressure of caesium vapor in excess of m1cron.

For the illuminating signal I have provided a special lamp 3%) which ismore particularly described in the application of Gjon Mlli, Serial No.125,548, filed February 13, 1939, for Incandescent filament and lamp. Inparticular, this lamp is very strong in the blue and ultraviolet portionof the spectrum. This lamp has a container of ultraviolet transmittingglass and has a very short tungsten filament 3| that operates at theorder of 7 amperes on a 10 volt circuit.

The result is that the filament operates at an excess of temperaturesuch as about 2800 or 2900 Kelvin, instead of the usual 2400 Kelvin withthe ordinary lamp. The reason for providing this lamp that is verystrong in the blue portion of the spectrum is, that the caesium has its5 tween light and dark is 40 volts or greater, while other photoglowtubes, with which I am familiar, operate at 5 or 10 volts difierence.The gas will be ionized and as a result the discharge will not bedestructive to the cathode as in tubes not constructed in accordancewith my invention, 30

when these tubes are attempted to be operated to supply current of theorder of milliamperes to actuate a relay. If some caesium should besputtered oil from my cathode, it will be replaced from the excesscaesium in the tube.

I prefer to utilize a mesh for the cathode, first, because it holds morecaesium than a cathode formed of solid material and, second, becauselight will pass through to the opposite caesium surface. The tube asdescribed operated satisfactorily with 15 milliamperes in the circuit.If the tube is operated on alternating current, then the discharge willstop when the light is withdrawn.

My photoglow tube is not to be confused with the usual gaseous phototubethat cannot be operated with a glow-discharge and which only producesmicroampere output.

Although a preferred embodiment of my invention has been disclosed, itwill be understood that many modifications may be made within the spiritand scope of the appended claim.

I claim:

A photosensitive device comprising a container, an anode and a cathodetherein, said cathode having caesium thereon, a gaseous atmosphereincluding one of the noble gases in said container, said gaseousatmosphere including caesium vapor having a pressure in excess ofmicron.

PHILIP W. BLACKBURN.

